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Selection of burst-like transients and stochastic variables using multi-band image differencing in the PAN-STARRS1 medium-deep survey.

Kumar, S. and Gezari, S. and Heinis, S. and Chornock, R. and Berger, E. and Rest, A. and Huber, M.E. and Foley, R.J. and Narayan, G. and Marion, G.H. and Scolnic, D. and Soderberg, A. and Lawrence, A. and Stubbs, C.W. and Kirshner, R.P. and Riess, A.G. and Smartt, S.J. and Smith, K.K. and Wood-Vasey, W.M. and Burgett, W.S. and Chambers, K.S. and Flewelling, H. and Kaiser, N. and Metcalfe, N. and Price, P.A. and Tonry, J.L. and Wainscoat, R.J. (2015) 'Selection of burst-like transients and stochastic variables using multi-band image differencing in the PAN-STARRS1 medium-deep survey.', Astrophysical journal., 802 (1). p. 27.


We present a novel method for the light-curve characterization of Pan-STARRS1 Medium Deep Survey (PS1 MDS) extragalactic sources into stochastic variables (SVs) and burst-like (BL) transients, using multi-band image-differencing time-series data. We select detections in difference images associated with galaxy hosts using a star/galaxy catalog extracted from the deep PS1 MDS stacked images, and adopt a maximum a posteriori formulation to model their difference-flux time-series in four Pan-STARRS1 photometric bands g P1, r P1, i P1, and z P1. We use three deterministic light-curve models to fit BL transients; a Gaussian, a Gamma distribution, and an analytic supernova (SN) model, and one stochastic light-curve model, the Ornstein-Uhlenbeck process, in order to fit variability that is characteristic of active galactic nuclei (AGNs). We assess the quality of fit of the models band-wise and source-wise, using their estimated leave-out-one cross-validation likelihoods and corrected Akaike information criteria. We then apply a K-means clustering algorithm on these statistics, to determine the source classification in each band. The final source classification is derived as a combination of the individual filter classifications, resulting in two measures of classification quality, from the averages across the photometric filters of (1) the classifications determined from the closest K-means cluster centers, and (2) the square distances from the clustering centers in the K-means clustering spaces. For a verification set of AGNs and SNe, we show that SV and BL occupy distinct regions in the plane constituted by these measures. We use our clustering method to characterize 4361 extragalactic image difference detected sources, in the first 2.5 yr of the PS1 MDS, into 1529 BL, and 2262 SV, with a purity of 95.00% for AGNs, and 90.97% for SN based on our verification sets. We combine our light-curve classifications with their nuclear or off-nuclear host galaxy offsets, to define a robust photometric sample of 1233 AGNs and 812 SNe. With these two samples, we characterize their variability and host galaxy properties, and identify simple photometric priors that would enable their real-time identification in future wide-field synoptic surveys

Item Type:Article
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Publisher statement:© 2015. The American Astronomical Society. All rights reserved.
Record Created:23 Aug 2016 11:05
Last Modified:02 Jun 2017 13:36

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